Improvement in electrical thermostats



1. H. GUEST.

Elctrical Thermostats. l l N0.139,95`3, PatentedJune17Ql873.

UNITED STATES PATENT OFFICE.

JOHN H. GUEST, OF BROOKLYN, NEW YORK, ASSIGNOB TO AUGUSTA GUEST, OF SAME PLACE.

IMPROVEMENT IN ELECTRICAL THERMOSTATS.

Specification forming part of Letters Patent No. 139,953, dated Juue 17, 1873; application filed March 29, 1873.

To all whom it may concern:

Be it known that I, JOHN H. GUEST, of Brooklyn, in the county of Kings and State of New York, have invented a new and Improved Fire-Alarm Thermometer, of which the following is a specication:

' The figure of the accompanying drawing represents a vertical section of my improved frrealarm thermometer for buildings and shipping.

The object of this invention is to construct a reliable instrument for closing the circuit of an electric fire-alarm as soon as the temperature of the surrounding air has reached a certain degree of heat.

The alarm-thermometers at present in use have the ends of the wires inserted in the ends of the glass or other vessels containing the mercury, but were insufficient and unreliable in their workings, as, on account of the changes in temperature, and the consequent unequal expansion of the wire and glass, atmospheric air was admitted into the instruments and prevented thereby the desired effect, so that the instruments failed in the object intended. My invention is intended to obviate these insuficiencies by connecting the end of one wire to the mercury of the instrument under a total exclusion of air; and consists of a bulb with an 'expansion-tube surrounded by an outer vessel, which is closed hcrmetically by a suitable liquid, cork, and sealing-wax. wire passes through this outer vessel and the bulb into the mercury, bein g in continuous Contact with it, the action of the instrument being thus not disturbed by th`e changes of temperature an d consequent access of air.

In the drawing, A represents the bulb or vessel containing the mercury 5 B, the expansiontube, extending vertically from the bulb A; O, the surrounding vessel or tube, forming one piece with the bulb A and tube B, extending to about two-thirds of the height of the latter, more or less. The conducting-wires D and E connect with a battery and suitable alarm instrument, the wire D being fused to the top end of the expansion-tube B, and inserted such a distance into it as to correspond with a fixed degree of heat, to which the ther mometeris adj usted. The end of wireE passes through the surrounding tube C and bulb A The end of the l to the mercury, being fusedin the glass of the same. The lower part of the tube C is then filled with some suitable liquid-preferably soluble glassand a cork, F, placed on it after the air between the cork and the liquid has been forced out along the expansiontube B by slow pressure on the cork. The cork is, for this purpose, perforated to close around expansion-tube B, and of concave shape at the bottom; and is covered and sealed, after the air has escaped to the expansion-tube and surn rounding vessel, by suitable cement or sealing-wax, so that no air can penetrate to the solution, and, still less, to the end of wire E, forming the contact with the mercury in bulb A.

Vhenever the temperature will rise to the degree to which the thermometer is adjusted the mercury will rise in the expansion tube, and, coming in con! act with the wire therein, establish the circuit and produce the alarm.

The small compass and neat appearance of the instrument allow its application to any part of the buildings or shipping, or to the walls or ceilings, as desired.

All mercurial bulbs heretofore made or patented, either by others or myself, in which a wire has been fused with the glass and in contact with the mercury, have been defective. I have had eight years practical experience in this business, and feel myself competent to judge correctly on this point.

I do not claim that this instrument will close an electrical circuit or ring a bell any better than a patented mercurial bulb granted to me October 12, 1869, No'. 95,796. That is not the object of this improvement. The operation of those put up by me and others is that, after tw-o or three years, the registering-point has become changedMas, for instance, when the bulb was made to close the circuit at 110O heat, it would, to the contrary, close it at a much less or lower point, varying' from 5O to 100. If made to close at 100O it was found to have changed its point to 90O and 950, Src. How to overcome this defect was the question. Other alarms were then made of metal, which do not register to the point at all 5 and the idea was conceived to burst a bulb, by which a circuit might be closed. Patent granted to fl, y

Augustus Guest, 1870, No. 108,352, and others before and since that time, all on the niercurial plan. Still the registering-point was not perfect.

Now, to make the old plan of fusing the Wire with the glass into the mercury prove to be a lasting instrument, I introduce a liquid to surround the Wire, and immerse that part of the bulb where the Wire is fused iu the bulb. This overcomes the trouble.

It will readily be seen that there is an unequal expansion between the metal Wire and glass; and, however little that inequality is, it does permit air getting in behind or into the mercurial bulb, and the air being so much more expansive drives the mercury up the tube beyond the iirst iixed point, and changes the designed point at which the circuit was intended to be closed. By the heat the wire expands, and, after it has contracted, there must be a space lett between the Wire and the glass, the wire having stretched, and no longer filling the hole in the glass, as it first did.

Now, I claim that surrounding this point with liquid prevents the air getting into the bulb. The air cannot get through the liquid to that point, as there cannot be space around the wire when the temperature increases or decreases.

What I desire to secure by Letters Patent is The sealed tube or vessel C, connected with the bulb A, iilled with a suitable liquid, and closed to exclude the air from the point of en,- trance of the Wire in the bulb A, substantially as and for the purpose specified.

JOHN II. GUEST. Witnesses:

PAUL GOEPEL, T. B. MosHEu. 

